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At least 1,063 records · Page 59Linked to original sources
PubMed1987

Receptor turnover and the action of 5-hydroxytryptamine on the salivary glands of the blowfly Calliphora erythrocephala, the housefly Musca domestica and frog skin epithelium.

1. Continual stimulation of frog skin epithelium and the salivary glands of the insects Calliphora and Musca with 5-hydroxytryptamine (5-HT) leads to desensitisation, i.e. the tissue fails to respond to the application of further 5-HT. 2. Incubation of desensitised frog skin and Musca salivary glands with either N-acetyl neuraminic acid or inositol partially restored the 5-HT responses whilst incubation with a combination of N-acetyl neuraminic acid and inositol gave additive effects on the recovery of the 5-HT responses. 3. Incubation of desensitised salivary glands of Calliphora with inositol totally restored the 5-HT response whilst incubation with N-acetyl neuraminic acid had no effect. 4. It is concluded that desensitisation involves depletion of secondary messenger from the tissues coupled with receptor degradation and that considerable differences exist in the turnover of 5-HT receptors, the receptors in Musca salivary glands being highly labile, those in Calliphora salivary glands highly stable and those of frog skin epithelium being intermediate in their stability.

Animals↗
PubMed1987

In vitro studies of the effects of naloxone on the root potentials in the frog spinal cord: enkephalin-like effect on the recurrent presynaptic inhibition.

Specific binding of [3H]naloxone was demonstrated in the frog spinal cord. In isolated and perfused frog spinal cord, naloxone increased the spontaneous discharges of the ventral root. Naloxone decreased the ventral root-dorsal root potential (VR-DRP) in a dose-dependent manner, and inhibited presynaptic inhibition of the ventral root reflex. Methionine-enkephalin also decreased the VR-DRP, and naloxone partially antagonized this effect. These results suggest the existence of enkephalinergic control of spinal motor activities and that naloxone has a partial agonistic effect in the frog spinal cord.

Animals↗
PubMed1990

Adaptive changes of H+ secreting cells in the epidermis of the leopard frog Rana pipiens.

1. Mitochondria-rich (MR) cells in the integument of the southern leopard frog, Rana pipiens, berlandieri, were stained with AgNO3 under a variety of environmental and metabolic treatment conditions known to increase H+ excretion rates across the skin. In this tissue AgNO3 proved to be a good stain for discriminating the MR cell populations from the granular cells. 2. High salinity adapted southern frogs showed no change in the MR cell population. The inability of the MR cell number to significantly increase suggested that the increased H+ excretion rates previously seen in these animals were not due to increased MR cell proliferation. 3. The MR cell population was found to increase in the NaNO3 adapted frogs, demonstrating the contribution of altered extracellular Cl- concentrations on the regulation of MR cell density. 4. Animals that were placed in chronic metabolic acidosis or pre-treated with ibuprofen demonstrated an increased MR cell population. The current observations are consistent with previous findings that these treatment regimes increase H+ excretion, suggesting that one of the cellular adaptive mechanisms responsible for increasing H+ excretion involves increasing the MR cell density. 5. The results further suggest that prostaglandins may play a role in regulating H+ excretion in MR cells, and that either changes in intracellular pH or prostaglandin formation regulates cell proliferation.

Adaptation, Physiological↗
PubMed1994

The androgen receptor mRNA is up-regulated by testosterone in both the Harderian gland and thumb pad of the frog, Rana esculenta.

Alpha 32P-labelled cDNA probe from plasmid containing rat androgen receptor (rAR) has been tested in hybridization experiments using RNAs from the Harderian gland and thumb pad of the edible frog, Rana esculenta. Northern blot analysis has shown a high degree of homology between the rAR cDNA and the frog androgen receptor mRNA (fAR mRNA); this has been supported by both the hybridization conditions (high stringency) and the molecular size of fAR mRNA which is quite similar to those described in mammals (9.4 kb). The role of androgens has been further investigated with respect to the kinetics of expression of fAR mRNA in in vivo experiments. In both the Harderian gland and thumb pad, testosterone has increased the levels of fAR mRNA as compared with the untreated groups. The use of cyproterone acetate (CPA) in combination with testosterone has resulted in a loss of the increase in fAR mRNA as compared to testosterone-treated groups, while CPA alone has resembled the control group. In primary cultures of frog Harderian gland and thumb pad cells, the steady-state levels of fAR mRNA have been increased in the cells exposed to testosterone as compared to those not exposed. These findings confirm that, in these androgen target tissues, testosterone exerts an up-regulation on its own receptors, increasing the accumulation of fAR mRNA in the same way as oestrogens up-regulate the expression of their own receptors in Xenopus liver and oviduct cells.

Animals↗
PubMed1994

Involvement of the cytoskeleton in the mechanism of action of endothelin on frog adrenocortical cells.

In a previous report, we have shown that endothelin-1 (ET-1) is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells. In the present study, we examine the possible involvement of cytoskeletal elements in the mechanism of action of ET-1 on corticosteroid secretion from frog adrenal gland. The microfilament disrupting agent cytochalasin B (5 x 10(-5) M) induced a reversible inhibition of the spontaneous secretion of corticosteroid and blocked the response of adrenocortical cells to ET-1 (5 x 10(-9) M). In contrast, the antimicrotubular agent vinblastine (10(-5) M) and the intermediate filament inhibitor beta-beta' iminodipropionitrile (10(-3) M) had virtually no effect on both spontaneous and endothelin-induced steroidogenesis. Taken together, these results indicate that, in the frog adrenal gland, the integrity of the microfilament network is required for the corticotropic activity of ET-1 whereas microtubules and intermediate filaments are apparently not involved in the mechanism of action of ET-1.

Adrenal Cortex↗
PubMed1996

Oxymetric and spectrophotometric study of the ascorbate oxidase activity shown by frog epidermis tyrosinase.

Many studies concerning the effect of ascorbic acid on the action of tyrosinase on several substrates have been carried out with contradictory results. The results shown in this work comprise a hypothetical reaction mechanism, which explains the ascorbate oxidase activity of frog epidermis tyrosinase. The reaction between frog epidermis tyrosinase and L-ascorbic acid was studied by oxymetric and spectrophotometric assays. The activity was linearly related to enzyme concentration, with a Michaelis constant for L-ascorbic acid of 0.160 +/- 0.009 mM and Vmax of 90 +/- 4 nM/s. Maximum activity was obtained at pH 7.5. The stoichiometry of the reaction was calculated by measuring the substrate (O2 and L-ascorbic acid) consumption as well as the initial rates of the consumption of oxygen and the disappearance of L-ascorbic acid. The stoichiometry was found to be 1:2 (O2:L-ascorbic acid). The action of the tyrosinase inhibitor tropolone was also studied. All the results present evidence concerning the ascorbate oxidase activity of frog epidermis tyrosinase and a possible reaction mechanism based on the different enzymatic forms of tyrosinase to explain such activity.

Animals↗
PubMed1974

Histological studies on the vestibular organ of frog embryos and larvae after simulated weightlessness.

The ontology of gravity receptors is discussed. As well as phylogenetic aspects of the question, we may ask whether the different gravity receptors in plants and animals derive from the same source; did they evolve from a general sensitivity of the living cell or do they represent parallel inventions. One may also ask whether during ontogeny of the receptor it receives information from gravity or whether the development of function of the organ is an autonomous process. In many cases ontogeny shows traces of phylogeny. Statoliths, e.g. the differentiating statolith membranes of the frog embryo, look somewhat like sedimentational structures. Furthermore the amphibian embryo in its relatively early stages takes up a special position in relation to the direction of gravity. Which mechanism is involved here? The materials studied were frog embryos and larvae which developed within a fast rotating clinostat. The results may help to answer the question as to whether the differentiation of the frog statolith membrane is an autonomous process.

Animals↗
PubMed2005

Possible autocrine regulation of chromaffin cell activity in adrenal glands of the frog by endothelin-1-induced serotonin release.

The aim of the present study was the demonstration of mechanisms of regulation of activity of chromaffin cells in the adrenal gland of Rana ridibunda (Anura-Amphibia). Previous studies have shown that endothelin-1 is an important factor for the maintenance of adrenal gland function. On the basis of these findings, frogs were injected with [Ala(1,3,11,15)]-endothelin-1 (0.025 mg/0.2 ml), which is a selective agonist of the endothelin B receptor, whereas control animals were injected with Ringer solution (0.2 ml). The adrenal glands were removed at 5, 20, and 60 min after injection and fixed, embedded in paraffin wax and stained by histological and immunohistochemical means, applied on adjacent 4-microm-thick sections. Sections were stained with hematoxylin and eosin for overall tissue analysis and, in parallel, serotonin was localized using the streptavidin-biotin complex technique while dopamine beta-hydroxylase and serotonin 2A receptors were shown by the peroxidase-antiperoxidase (PAP)-3,3'-diaminobenzidine tetrachloride (DAB) method. After injection of [Ala(1,3,11,15)]-endothelin-1, chromaffin cells secreted serotonin and synthesized dopamine beta-hydroxylase. In conclusion, these findings suggest that [Ala(1,3,11,15)]-endothelin-1 stimulates chromaffin cell activity in frog adrenal glands. Moreover, the presence of serotonin 2A receptors in chromaffin cells indicates that these cells are also targets for serotonin and that there is an autocrine signaling pathway in chromaffin cells. This is the first report providing data on the effects of endothelin-1 on chromaffin cells in frog adrenal glands.

Adrenal Glands↗
PubMed2006

Possible role of insulin-like growth factor-II C-peptide on catecholamine release and ultrastructural aspects of chromaffin cells in the adrenal gland of the frog.

The present study was undertaken to demonstrate that insulin-like growth factor-II C-peptide (IGF-II C-peptide) affects the function of the adrenal gland of Rana ridibunda (Anura, Amphibia) by stimulating chromaffin cells. Previous studies have shown that insulin-like growth factors affect adrenal gland function in mammals. On the basis of these findings, frogs were injected with IGF-II C-peptide (2.5 microg/0.2 ml), whereas control animals were injected with Ringer solution (0.2 ml). The adrenal glands were removed at 12 and 48 h after injection and fixed, embedded in paraffin wax and Epon, and examined by immunohistochemistry and transmission electron microscopy to investigate whether there were structural changes and activation of chromaffin cells in the frog adrenal gland. Sections were stained with hematoxylin and eosin for overall tissue analysis and, in parallel, serotonin was localized using the streptavidin-biotin complex technique while dopamine beta-hydroxylase was shown by the peroxidase-antiperoxidase-3, 3'-diaminobenzidine tetrachloride method. After injection of IGF-II C-peptide, chromaffin cells released serotonin and synthesized dopamine beta-hydroxylase. The most pronounced effect of IGF-II C-peptide on the chromaffin cells was observed at 12h after injection. Our results indicate that there is a possible role of IGF-II C-peptide on chromaffin cell activity enhancing catecholamine release in the adrenal gland of the frog.

Adrenal Glands↗
PubMed2004

The ascaphins: a family of antimicrobial peptides from the skin secretions of the most primitive extant frog, Ascaphus truei.

The tailed frog Ascaphus truei occupies a unique position in phylogeny as the most primitive extant anuran and is regarded as the sister taxon to the clade of all other living frogs. Eight structurally related peptides, termed ascaphins 1-8, were isolated from norepinephrine-stimulated skin secretions of A. truei and were shown to possess differential growth inhibitory activity against Escherichia coli and Staphylococcus aureus. Ascaphins 2-7 may be represented by the consensus amino acid sequence GX2DX2KGAAKX3KTVAX2IANX.COOH whereas ascaphin-1 (GFRDVLKGAAKAFVKTVAGHIAN.NH2) and ascaphin-8 (GFKDLLKGAAKALVKTVLF.NH2) contain a C-terminally alpha-amidated residue. The ascaphins show no appreciable structural similarity with other families of antimicrobial peptides from frog skin but display limited sequence identity with the cationic, amphipathic alpha-helical peptides pandinin 1 and opistoporin 1, isolated from the venoms of African scorpions. Ascaphin-8 shows the highest potency against a range of pathogenic microorganisms but has the greatest haemolytic activity. The data indicate that the host defence strategy of using antimicrobial peptides in skin secretions arose early in the evolution of anurans.

Amino Acid Sequence↗
PubMed2006

Serotonergic modulation of synaptic transmission and action potential firing in frog motoneurons.

Frog spinal neurons receive a prominent innervation from the bulbar serotonergic nuclear complex. We used an isolated spinal cord preparation to examine the effect of serotonin (5-hydroxytryptamine, 5-HT) receptor activation on segmental and descending monosynaptic excitatory inputs to frog lumbar motoneurons. Bath-application of 5-HT (0.05 mM) caused a significant reduction in the peak amplitude of segmental EPSP elicited by dorsal root (DR) stimulation (P < 0.05). Contrasting to DR evoked responses 5-HT did not affect the descending monosynaptic EPSP conditioned by ventrolateral column (VLC) stimulation. Recording of the VLC induced EPSP-spike (E-S) field response within the ventral horn motor nucleus disclosed a substantial enhancement in the population discharge of motoneurons upon 5-HT application (P < 0.05). These data suggest the potential importance of serotonergic receptors in motor integration and gaining of motor output in the frog spinal cord.

Action Potentials↗
PubMed2005

Effects of prey type on specific dynamic action, growth, and mass conversion efficiencies in the horned frog, Ceratophrys cranwelli.

To be most energetically profitable, predators should ingest prey with the maximal nutritional benefit while minimizing the cost of processing. Therefore, when determining the quality of prey items, both the cost of processing and nutritional content must be considered. Specific dynamic action (SDA), the increase in metabolic rate associated with feeding in animals, is a significant processing cost that represents the total cost of digestion and assimilation of nutrients from prey. We examined the effects of an invertebrate diet (earthworms) and a vertebrate diet (newborn mice) on mass conversion efficiencies, growth, and SDA in the Chacoan horned frog, Ceratophrys cranwelli. We found the earthworm diet to be significantly lower in lipid, protein, and energy content when compared to the diet of newborn mice. Growth and mass conversion efficiencies were significantly higher in frogs fed newborn mice. However, mean SDA did not differ between frogs fed the two diets, a finding that contradicts many studies that indicate SDA increases with the protein content of the meal. Together, our results indicate that future studies evaluating the effect of meal type on bioenergetics of herpetofauna are warranted and may provide significant insight into the underlying factors driving SDA.

Animal Nutritional Physiological Phenomena↗
PubMed2005

Polychlorinated biphenyls, sex steroid hormones and liver retinoids in adult male European common frogs Rana temporaria.

Declines in amphibian populations and species biodiversity during the last decades has called for an assessment of possible threats to these animals. Polychlorinated biphenyls (PCBs) are known endocrine disrupting contaminants and are found in high levels in some populations of wild living amphibians. To evaluate the endocrine disrupting potential of PCBs in adult frogs, Aroclor 1,254 were subcutaneously injected into male European common frogs Rana temporaria. The injected doses ranged from 0.01 to 100 mg/kg body mass, resulting in liver concentrations between 74 and 133,619 microg/kg ww. After 14 days, serum testosterone (T), estradiol (E) and hepatic retinol (R) and retinylpalmitate (RP) were easured. No dose dependent effects were found on levels of hormones or retinoids. However, a significantly higher within-group variation in the E-T ratio in the exposed groups may indicate that the sex-hormone homeostasis of male R. temporaria is affected by PCBs shortly after arousal from hibernation, but that the effects are subtle and that several different mechanisms are involved. The lack of direct effect on T, E, R and RP may be due to the timing of exposure (shortly after arousal from hibernation), or due to a relatively short exposure time to Aroclor 1,254. Based on the results, we propose that future research should focus on effects of PCBs in relation to the different physiological phases frogs experience throughout the year (hibernation, reproduction etc.).

Animals↗
PubMed2006

Assessing the effects of the three herbicides acetochlor, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4-dichlorophenoxyacetic acid on the compound action potential of the sciatic nerve of the frog (Rana ridibunda).

To assess the relative toxicity of the herbicides acetochlor and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on the nervous system, the sciatic nerve of the frog (Rana ridibunda) nerve was incubated in saline inside a specially designed recording chamber. This chamber permits monitoring of the evoked compound action potential (CAP) of the nerve, a parameter that could be used to quantify the vitality of the nerve in normal conditions as well as when the nerve was exposed to the compounds under investigation. Thus, when the nerve was exposed to acetochlor, the EC(50) was estimated to be 0.22mM, while for 2,4,5-T the EC(50) was 0.90mM. Using the identical nerve preparation, the EC(50) of 2,4-D was estimated to be 3.80mM [Kouri, G., Theophilidis, G., 2002. The action of the herbicide 2,4-dichlorophenoxyacetic acid on the isolated sciatic nerve of the frog (Rana ridibunda). Neurotoxicol. Res. 4, 25-32]. The ratio of the relative toxicity for acetochlor, 2,4,5-T and 2,4-D was found to be 1:4:17.2. However, because it is well-known that the action of 2,4-D is dependent on the pH, the relative toxicity of the three compounds was tested at pH 3.3, since it has been found that the sciatic nerve of the frog is tolerant of such a low pH. Under these conditions, the EC(50) was 0.77mM (from 0.22mM at pH 7.2) for acetochlor, 0.20mM (from 0.90mM) for 2,4,5-T and 0.24mM (from 3.80mM at pH 7.2) for 2,4-D. Thus, the relative toxicity of the three compounds changed drastically to 1:0.25:0.31. This change in the relative toxicity is due not only to the increase in the toxicity of 2,4,5-T and 2,4-D at low pH levels, but also to the decrease in the toxicity of acetochlor at pH 3.3.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed2005

Generation of a long-lasting, protective, and neutralizing antibody response to the ranavirus FV3 by the frog Xenopus.

Xenopus serves as an experimental model to evaluate the contribution of adaptive immunity in host susceptibility to emerging ranaviral diseases that may contribute to amphibian population declines. It has been previously shown that following a secondary infection with the ranavirus frog virus 3 (FV3), adult Xenopus more rapidly clear FV3 and generate specific anti-FV3 IgY antibodies. We have further evaluated the potency and persistence of the Xenopus antibody response against FV3. Frogs inoculated with FV3 (without adjuvant) up to 15 months after priming produce specific, thymus-dependent anti-FV3 IgY antibodies detectable from 10 days to 8 weeks post-infection. These antisera from boosted frogs are neutralizing in vitro and provide partial passive protection to susceptible larvae when they are injected a few minutes before FV3 inoculation. These results with Xenopus suggest that other anuran amphibians are likely to develop effective long-lasting protective humoral immunity after an initial viral exposure.

Animals↗
PubMed2024

Horizontal plasmid transfer promotes antibiotic resistance in selected bacteria in Chinese frog farms.

The emergence and dissemination of antibiotic resistance genes (ARGs) in the ecosystem are global public health concerns. One Health emphasizes the interconnectivity between different habitats and seeks to optimize animal, human, and environmental health. However, information on the dissemination of antibiotic resistance genes (ARGs) within complex microbiomes in natural habitats is scarce. We investigated the prevalence of antibiotic resistant bacteria (ARB) and the spread of ARGs in intensive bullfrog (Rana catesbeiana) farms in the Shantou area of China. Antibiotic susceptibilities of 361 strains, combined with microbiome analyses, revealed Escherichia coli, Edwardsiella tarda, Citrobacter and Klebsiella sp. as prevalent multidrug resistant bacteria on these farms. Whole genome sequencing of 95 ARB identified 250 large plasmids that harbored a wide range of ARGs. Plasmid sequences and sediment metagenomes revealed an abundance of tetA, sul1, and aph(3&#x2033;)-Ib ARGs. Notably, antibiotic resistance (against 15 antibiotics) highly correlated with plasmid-borne rather than chromosome-borne ARGs. Based on sequence similarities, most plasmids (62%) fell into 32 distinct groups, indicating a potential for horizontal plasmid transfer (HPT) within the frog farm microbiome. HPT was confirmed in inter- and intra-species conjugation experiments. Furthermore, identical mobile ARGs, flanked by mobile genetic elements (MGEs), were found in different locations on the same plasmid, or on different plasmids residing in the same or different hosts. Our results suggest a synergy between MGEs and HPT to facilitate ARGs dissemination in frog farms. Mining public databases retrieved similar plasmids from different bacterial species found in other environmental niches globally. Our findings underscore the importance of HPT in mediating the spread of ARGs in frog farms and other microbiomes of the ecosystem.

Animals↗
PubMed2005

The complete mitochondrial genome of a tree frog, Polypedates megacephalus (Amphibia: Anura: Rhacophoridae), and a novel gene organization in living amphibians.

In this study, we have determined the complete sequence of the mitochondrial genome of an Old World tree frog Polypedates megacephalus (Anura: Rhacophoridae) by using a long polymerase chain reaction (PCR) technique and shotgun strategy of sequencing. The entire mtDNA sequence is 16,473 nt long with a novel mitogenomic gene organization in amphibians. Unlike other neobatrachian frogs, the transfer ribonucleic acid (tRNA)-Leu(CUN) and tRNA-Thr genes exchange their positions in P. megacephalus and form a Thr-Leu(CUN)-Pro-Phe tRNA gene tetrad. Moreover, we found that the ATP8 gene was replaced by a noncoding sequence of 853 nt long and that the ND5 gene was absent in the new mitogenome. These peculiar features of P. megacephalus mtDNA were further studied among related anuran species by PCR amplification. The new sequence data was used to assess the phylogenetic relationships of the three living amphibian orders using neighbor-joining, maximum likelihood, and Bayesian methods. In agreement with most morphological studies, phylogenetic analyses of a whole mitochondrial genome data set suggest a close relationship between salamanders and frogs. Moreover, using a molecular clock-independent Bayesian approach for inferring dating information from molecular phylogenies, we have provided a rough timescale for living amphibian evolution. This timescale provides a working framework for future paleontological researches on amphibian evolution and improves our understanding of the evolutionary history of modern amphibians.

Animals↗
PubMed2004

Estimation of radiation doses from (137)Cs to frogs in a wetland ecosystem.

Currently, there is no established methodology to estimate radiation doses to non-human biota. Therefore, in this study, various dose models were used to estimate radiation doses to moor frogs (Rana arvalis) in a wetland ecosystem contaminated with (137)Cs. External dose estimations were based on activity concentrations of (137)Cs in soil and water, considering changes in habitat over a life-cycle. Internal doses were calculated from the activity concentrations of (137)Cs measured in moor frogs. Depending on the dose model used, the results varied substantially. External dose rates ranged from 21 to 160 mGy/y, and internal dose rates varied between 1 and 14 mGy/y. Maximum total dose rates to frogs were below the expected safe level for terrestrial populations, but close to the suggested critical dose rate for amphibians. The results show that realistic assumptions in dose models are particularly important at high levels of contamination.

Animals↗